This invention relates to the pyrolytic destruction of waste materials, and in particular, to a method and apparatus for disposing of toxic or hazardous materials, such as polychlorinated biphenyls (PCB's).
There are a growing number of toxic or hazardous compounds the use of which is being withdrawn or prohibited because of irreversible harm to health or the environment. These materials must be managed and disposed of effectively. In addition to polychlorinated biphenyls, there are also organophosphorous, organonitrogen and organometallic compounds, as well as other materials, that exist in massive quantities and demand effective means of disposal. The majority of the toxic compounds are in a composite matrix format often combining organic and inorganic components or fractions, and in these cases, little or no disposal technology is available. PCB laden capacitors are a good example of a composite matrix waste requiring safe and efficient disposal methods.
Various methods have been tried for disposing of toxic wastes, including thermal destruction, chemical detoxification, long-term encapsulation and specific land fill methods. With the exception of high temperature incineration, little success has been demonstrated for the safe disposal of highly toxic or extremely persistent wastes, such as PCB's. The methods that have been tried have either not been able to handle anything but homogeneous waste feeds streams, or they have only been able to handle relatively low concentrations of toxic compounds in the waste materials. Further, very few of the disposal methods tried to date have been able to be developed to operate on a commercial scale, because it generally has not been possible to demonstrate to the various regulatory agencies that the disposal methods used in the past have been completely safe.
Of the many methods tried for the disposal of toxic or hazardous wastes, thermal destruction has been the most promising. However, the toxic waste materials are usually very stable organic molecules, and they require long dwell times at high temperatures to effect thermal destruction. Some combustion or incineration systems can achieve the necessary conditions, but the facilities required are very large scale, and often the products of the combustion process present as much of a disposal problem as the original toxic wastes.
In the past, attempts have been made to use electric plasma arcs to destroy toxic wastes. An electric plasma arc system, being essentially pyrolytic, overcomes many of the deficiencies of an incineration or combustion process, in that the volume of gaseous products produced is much less, so the equipment is substantially smaller in scale. Laboratory demonstrations have shown that a plasma arc is capable of atomizing and ionizing toxic organic compounds, and that these atoms and ions usually recombine into simple products. While residual toxic materials are formed, these can be captured, so that no significant amount of toxic materials is released to the environment.
Until the present invention, however, there has not been produced a commercially viable method for the pyrolytic destruction of waste materials with sufficiently high reliability and efficiency to satisfy regulatory authorities that this method of waste destruction is safe.